The rhetoric between the two has heated up in recent days, and reached a new level after the rivals finished in a virtual tie in the Iowa caucuses on Monday.

Sanders on Tuesday called out Clinton when asked in New Hampshire if she was a progressive. “Some days, yes. Except when she announces that she is a proud moderate, and then I guess she is not a progressive,” he responded.

Clinton, for her part, has tried to twist the words into a positive for her. “It was kind of a low blow … so I thought to myself, I think it was a good day for progressives when I helped to get 8 million kids health care under the children’s health insurance program and I think it was a good day for progressives when I joined with colleagues in the senate to stop George W. Bush from privatizing social security,” she said Wednesday on the campaign trail. “It was another good day when I went out to Geneva to speak out on behalf of gay rights and Beijing to speak out on behalf of women’s rights.”

“There have been a lot of good days,” Clinton said as she continued to list her policies and endorsements, and talked optimistically about her chances in Tuesday's New Hampshire primary. “So I hope we keep it on the issues because if it’s about our records, hey I’m going to win by a landslide on Tuesday.”

The Clinton campaign has maintained that Sanders has broken his rule of not going negative on an opponent, but Sanders' team say he is just highlighting policy differences.